For improving the collision safety of automobiles, the bodies of automobiles are reinforced and air bags are provided in automobiles these days. In the field of automobiles, however, the most important matter is to reduce the fuel consumption for saving resources and for solving environmental problems. To meet it, lightweight automobiles are much desired. For reducing the body weight of automobiles, many their parts are made of resin and not metal, and the conversion from metal to resin for them is remarkable these days. For automobile parts, thermoplastic resins such as polypropylene resins and the like are being much used in place of conventional fiber-reinforced thermosetting resins (FRP), since their moldability is good and their moldings have high mechanical strength and rigidity and since they are recyclable and applicable to various parts.
The requirement for reducing the body weight of automobiles is being severer day by day. For reducing the weight of moldings for automobile parts, much tried are various techniques of reducing the wall thickness of the moldings. However, for reducing the wall thickness of resin moldings, the melt fluidity of the resin melt for the moldings must be increased in addition to the mechanical strength and the rigidity characteristic of the resin moldings. For that object, various techniques have heretofore been proposed of adding other thermoplastic resins or thermoplastic elastomers to polypropylene resins and adding a reinforcing agent such as glass fibers or the like or adding a filler such as talc or the like thereto, to thereby further enhance the mechanical strength and the rigidity of polypropylene resins.
Regarding the improvement in the collision safety of automobiles, the requirement of high-level safety for protecting drivers and passengers from not only conventional head-on collision but also side-on collision is increasing. Of automobiles, doors are the most important constituent members for ensuring the safety of drivers and passengers from side-on collision.
In the door system of automobiles, heretofore, the door trim to form the interior surface-member is made of polypropylene resin or the like in a mode of injection molding of the resin. To reduce the shock in the side-on collision of automobiles, a shock absorbent is disposed between the inner door panel and the door trim. For example, (1) Japanese Patent Laid-Open No. 69780/1993 discloses a trim substrate having a hollow and granular energy absorbent capable of undergoing plastic deformation or brittle fracture inserted thereinto. (2) Japanese Utility Model Registration No. 259345 discloses a door panel for vehicles having a cushionable foam layer formed on the inner surface of its trim. (3) Japanese Patent Laid-Open No. 11829/1997 discloses a technique of inserting an inner member for vehicles (shock eliminator) into the space between an inner door panel and a door trim, in which the shock eliminator is tabular and is provided with lattice ribs on its one surface or both surfaces.
As compared with the structures (1) and (2), the structure (3) is easy to produce and does not require so much labor for its fabrication, and its productivity will be therefore good. For this, however, the shock eliminator with lattice ribs formed thereon must be produced separately in a mode of injection molding, and, in addition, it requires an additional step for inserting it into the space between an inner door panel and a door trim. Therefore, the productivity of (3) is not always so good.
The door trims disclosed are generally produced in a mode of injection molding or injection compression molding, and their trim structures may be integrally molded for good design. However, in the molding method for them, the melt fluidity of thermoplastic resin for them has a great influence on their moldability. Therefore, for reducing their weight and wall thickness, the molecular weight of the usable thermoplastic resin is limited, and, in addition, the characteristics including the impact resistance of the resin could not be utilized with no limitation. A different blow-molding method for producing door trims is known.
For example, (4) Japanese Patent Laid-Open No. 238664/1996 discloses a method for producing at a time two door trims for the left and right sides of a vehicle, which comprises blow-molding a door trim structure integrated with a weather strip-fitting flange, followed by cutting it into two. (5) Japanese Patent Laid-Open No. 89211/1984 discloses a method for producing a blow-molded door trim having air inlet openings and a large number of air outlet holes all for air conditioning through its side surface, for which is used a mold with a number of hole-forming pins aligned on its inner surface.
(6) Japanese Patent Laid-Open No. 164740/1996 discloses a door trim for automobiles that runs over an inner door panel in the waist part of an automobile door to cover it. This is made of a blow-molded structure with partition walls formed in its inner space. In this, a foaming resin material is injected into some hollow spaces, and foamed therein, and the resulting resin foam filled in these spaces acts as a shock absorber. The door panels disclosed are produced in a mode of blow molding, but they all substantially follow the constitution of conventional door trims. Concretely, in these, the inner door panel and the door trim are different members. Optionally combined with a shock absorber disposed therebetween, they are assembled into a door trim structure. To that effect, the door trim structure does not differ at all from conventional ones.
Specifically, the conventional technical idea for fabricating the trim member of the door system for automobiles is merely such that only the interior door trim for automobiles is made of thermoplastic resin so as to reduce its weight, and does not reach an advanced idea of forming the entire door trim structure out of thermoplastic resin. The reason will be because the mechanical strength of thermoplastic resin is not satisfactory and the molding method for the resin is limited, and because the inner door panel must satisfy not only the material function of ensuring the mechanical strength and toughness enough for door panels but also the constitutional function of fitting thereto various functional devices including a door windowpane sliding (automatic) device, a door opening and shutting device, a door locking device, speakers and other members.
The present invention is to provide a door trim structure for automobiles, of which the advantages are that it is lightweight and simple, it is resistant to side-on collision, it can be formed in a mode of integral molding and its productivity is good, the number of elements constituting it is greatly reduced, it does not require much labor and energy for constructing it into doors, and it is recyclable.